Electronics > Repair

1502DD Lab power supply repair

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Swake:
Nah, the 14 pin chip is not a 723:
- pin 8 on the 723 does nothing, while on the schematic it is powering a green LED.
- On the 723 pin 12 is for Vcc while here it is likely an analog input as there is the current potentiometer WR3

Small error in the schematic: pin 1 (input) en pin 3 (output) of the 78M05 are reversed.

Yig666:
Thank you for help

As Swake pointed out, there is a schematic error: pin 1 (input) and pin 3 (output) of the 78M05 are reversed
I know about the 1502DD schematic which uses the 14-pin LM723, but I check my PCB and as Swake pointed out, the 14-pin IC "U2" has different pinout.
The 14 pin IC "U2" does not have the label removed like "U3" and "U4", it looks like it comes from the factory without a label.
Anyway, if after replacing the LM358 integrated circuit it still doesn't work, I'll give up and go buy another power supply.

max.wwwang:
No don’t give up though go for a new one if needed.  :)

Posting the new supply on sale was just so everyone knows what this thing looks like (as I would normally want).

Yig666:
Update:
I replaced the LM358 IC and now the power supply works.

All the effort I put into reverse engineering the schematic and figuring out what the problem was wasn't worth it for a cheap power supply, but I learned to use the hot air station and to use KiCad and the fact that I gained experience is more important.

When I soldered the IC, the pcb started to swell (blistering), I don't know why, the temperature of the hot air station was around 250-300 degrees Celsius, I tried to lower the temperature but the solder didn't melt, at the end of the day it doesn't matter as long as the power supply works.

Thanks to everyone who helped me.

Swake:
 :-+

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